One of important functions of a welding robot is weaving. As is well known in the art, such weaving is a welding method of oscillating a welding torch substantially perpendicularly to a weld line to move the same along the weld line. In a conventional control method for making the welding robot such weaving, generally the oscillation width in the perpendicular direction, i.e., the weaving width amplitude is previously set in a computer as a constant value, to oscillate the forward end of the torch of the welding robot in the constant weaving amplitude thereby to perform welding.
However, in the workpiece to be welded (hereinafter referred to as "welded member", and two welded members to be welded to each other are expressed as "first" and "second" ones respectively), the butting space and bevel width between the first and second welded members (generically referred to as "interspace" between the welded members) are frequently non-uniform in the weld line direction due to variations and integrated errors in cutting accuracy, bending accuracy and assembling accuracy caused by bending and distortion of materials. When such welded members are woven by a welding robot through application of the conventional control method, welding is performed in the constant weaving amplitude regardless of the non-uniformity, whereby under-and-overwelding is caused depending on positions, to extremely lower the weld quality.
Therefore, manual welding has been generally required to weave welded members having non-uniform interspace.